I once did a comparison of 22s at a particular position in our state - PBR rankings vs PG rankings.
Some kids were on both lists whereas some kids were on one and totally left off another.
How? Simple...parents weren't willing to pay for showcases at both and they ain't going to list you if you never attended an event.
My kid was ranked (in his position for our state) #6 in one and #8 in another. Pretty much the same. IIRC the top 2 or 3 in both were same kids. But there was a lot of differences in the rankings too.
To the coaches question...I would have said that coaches don't care about the rankings. But, just recently I saw a tweet by a coach talking about how happy they were to have an incoming player and he specifically mentioned his ranking. So, maybe some do look at it?
Personally, I think the rankings are like spring training statistics. Great to have good ones. Not necessarily meaning anything if you have bad ones. And none of it means anything when the real stuff starts.
One thing I would stress is that it all varies from state to state. In some states the PBR and PG guys are great. In others, not so much. It's not consistently administered across the country.